Hacksaws and Their Parts
There are types of hand saws for cutting wood and metal. They are cutting tools shaped like a thin blade, toothed on one or both edges.
The topics covered in this article are as follows:
Saw Frames
Used to mount the cutting blade for hand cutting operations. There are two types: fixed saw frames and adjustable saw frames. Adjustable ones can be adjusted to fit saw blades 200-400 mm in length.
Saw Blades
Made of tool steel (WS) or high-speed steel (HSS), their outer sections are hardened for durability. They are toothed on one or both edges.
The shape, angles, and set of the teeth are varied depending on the properties of the material to be cut.
If the tooth pitch is small, the teeth will be finer and more numerous, so the cutting durability increases. For this reason, a higher tooth count (small pitch) is chosen for hard materials, and a lower tooth count (large pitch) for soft materials.
To prevent the saw blade from overheating and binding in the kerf it cuts, the teeth are set. Setting the teeth individually or in groups makes the kerf wider than the blade thickness.
Tooth Pitch on a Saw Blade
The coarseness or fineness of saw teeth is expressed by the number of teeth per inch (1″), in short, the saw’s pitch. The saw’s pitch is obtained by dividing the length of one inch by the number of teeth in that inch.
Choosing a Blade According to the Material to Be Cut
Solid materials are cut with coarse-tooth saws. Hollow materials with thick walls are cut with medium-tooth saws. Thin materials like pipe and sheet metal are cut with small-pitch saws.
Rules for Cutting with a Hacksaw
The following points should mainly be observed when cutting with a saw:
For a smooth cut, the saw teeth must face forward and be tensioned adequately with the wing nut. (Neither too little, nor too much)
To start the cut, a guide notch should be opened by tilting the saw forward at an angle of about 5-10°. To open this notch, the saw blade can be rested against the thumb, or a triangular file can also be used. The saw should be drawn under its own weight until it makes its own mark.
While the saw is pushed forward with the left hand, the right hand applies just enough pressure to cut; the left hand also provides balance. Pressure is released while the saw is drawn back. The return stroke speed is faster than the cutting speed.
The part should be cut correctly, following the marking line. (Be careful not to cut exactly along the marking line.)
Parts should be cut on their wider surface. On a narrow surface, since fewer teeth will be doing the cutting, the saw blade is strained.
The workpiece should be clamped so that it doesn’t vibrate during cutting, and should not overhang the vise jaws by too much. If cutting is done far from the vise jaws, a shrill and unpleasant noise occurs.
Oil should not be used when cutting with hand saws. This is because oil prevents the chips from flowing out and causes them to jam.
During cutting, the full length of the saw should be used; only a portion of the saw shouldn’t be used.
When cutting thin parts with a wide surface, the cut is made from the wide surface. If cut from the narrow surface, the pressure force will be distributed among fewer teeth, increasing the force on each individual tooth. In this case, the teeth may break.
Saw Maintenance
As with all other sheet metal materials, storing saw blades lightly oiled is suitable to prevent rusting.
This is related to using saws in accordance with technological rules; mistakes should not be made, but potential errors should also be known.
After finishing the cutting operation, the saw’s wing nut is loosened by about one turn. This is to prevent the saw blade from remaining constantly under tension. A blade left under tension for a long time becomes fatigued and breaks more easily.
Safety Precautions When Cutting with a Hacksaw
- Cutting should not be continued with a different blade in a kerf started by another blade. This causes binding and breakage.
- The part should not be snapped off toward the end of the cut. Otherwise, the part will fly off and create a hazard.
- If pressure isn’t reduced toward the end of the cut, the saw suddenly breaking free can cause an accident.
- Cutting position, cutting height, and body balance should be appropriate.
- Cutting speed should be set to around 60 strokes per minute.
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